If only a few engineers are using it out of their own volition that I don't think that justifies trying to imply that Google is a customer.

Pretty misleading and underhanded I think.

I work at one of those companies (not google) and Polypane is actively banned as “not safe, shouldn’t be used at all”.

Not to take away from the product, which does look cool, but the “customer list” is definitely sketchy.

Fair point. I'm just explaining how Polypane might have rationalized the positioning.